Thermally responsive electric circuit breaker



g- 4, 1964 B. c. VON PLATEN 3,143,618

THERMALLY-RESPONSIVE ELECTRIC CIRCUIT BREAKER Filed June 5. 1961 EaZI-zar Carl Van. platen. aw

near to the electrodes.

United States Patent 3,143,618 THERMALLY RESPONSIVE ELECTRIC CIRCUIT BREAKER Baltzar Carl von Platen, Gotgatan 16, Stockholm, Sweden Filed lane 5, 1961, Ser. No. 114,867 Claims priority, application Sweden June 11, 1960 6 Claims. (Cl. 200-137) The present invention relates to an electric circuit breaker which has the advantage of being inexpensive to manufacture and of simple construction while having decided advantages. The contact pressure between the electrodes which close the circuit, is constant or practically constant until the moment of circuit-breaking. The movement of that element which transmits the impulse to the means for breaking or closing the circuit, is very small as compared to the movement of the electrodes. The circuit breaker is able to break even very substantial amperages of direct current-alternating current is always easier to break.

Because of the above-mentioned advantages and the low price at which the device can be made and sold, the circuit breaker can be used as one of the main parts in a thermostat, or more specifically, in an instrument for making and breaking an electric current in response to temperature changes, such as for example, in a refrigerator or a heating device. In the former case the instrument may be referred toas an electric refrigeration thermostat or as a refrigeration thermostat. In the latter case, it may be termed a heating thermostat. Such thermostats will usually be less expensive when they are built as a very compact unit. However, this means that the sensing medium, which expands and contracts as the temperature varies, will be close to or relatively It also means that the problem of constantcontact pressure between the electrodes has to be solved in asimple and inexpensive way because in case the contact pressure mentioned would slowly sink to zero before breaking, heat would be generated. Consequently, as known, the thermostat would break and net that is acted upon by an element for the instantaneous closure of a circuit or breaking of the same, and wherein a movable contact acted upon by the magnet is maintained in an open position by a spring whose force in the closed position is less than that of the magnetic force, and wherein the said magnet, when the circuit is closed, is acted upon by a supporting force in opposi tion to the magnetic force, from a fixed part of the cir-.

cuit breakersbase, and wherein the same magnet is connected with said sensing element through the medium of a spring.

The invention will now be described with reference to FIGURES 1 to 5, wherein FIG. 1 shows a section parallel with and through the geometric axis of a refrigeration thermostat, to which 'the invention is applied;

FIG. 2 shows a cross section along the line IIII of FIG. 1;

FIG. 3 shows a cross section alongthe lineIIlIII;

FIG. 4 shows a cross section along the line IVIV, and

FIG. 5 .shows a section parallel with and through the geometric axis of a heating type of thermostat, to which thermostat the invention is applied.

In FIG. 1a soft rubber or thermally responsive sensory component is designated 1. The main body or casing of the thermostat, suitably of aluminum, is designated 2. A disc 3 is permanently held pressed against step 4 by the pressure in the rubber. The disc 3 has a central lip 5 whose outer surface should best be conic. Its ring-shaped surface 8 should be as narrow as possible radially. It (8) should thus be or approximate a sharp edge. The central portion of piston 9 has a smaller diameter than the cylinder in which the piston moves, which gives rise to the existence of a small chamber 10. The breadth or height h of the contact surface between the cylinder and the part of the piston is very small, preferably less than & of the cylinders diameter. The

functions of the conic surface 6, chamber 10 and the this in turn against the axle 21. The thermostat may be set for different temperatures by means of turning the wheel 22. The thermostat is mounted in the plate 23, which is part of the refrigerator. A stud 24 and a tag 25 prevent the wheel from being turned more than Chamber 27 contains the electric con- A thin elastic disc 29 of an electrically one revolution. tact breaker.

insulating material, suitably mica, prevents electric contact between current-carrying components and the metal parts of the thermostats assembly (9, 3, 2). The circuit is closed when the electrodes 30a and 3012 (see also FIG. 3) are short circuited across the silver strip 31, which is attached to the leaf spring 32 loosely enough to allow a little play. The electric leads 33a and 33b pass through a sealing plug 34 of glue, suitably a synthetic resin like epoxy, also called Araldite. A thin-walled cup 35 used solely for the purpose of moulding the plug 34 is allowed to remain in situ. A foundation 36, suitably of Bakelite, supports not only the electrodes 30a and 30b but also the two bent leaf springs 32 and 37, which are both fixed to it by means of the rivet 38. These springs may sometimes be made as one piece, but as springs, they are nonetheless two entities. Leaf spring 37 may be said to consist of two parts, an inner and an outer part.

The inner part reaches from the attachment point or rivet 38 as far as the geometric axis of the piston 9, which in this case at least, may be considered to coincide with that of the thermostat. The permanent magnet 40 is fixed to the outer part of said leaf spring 37, and the iron armature 41 to leaf spring 32. When the circuit is closed, the position of the magnet is fixed by a mechanical stop on the foundation. This is suitably arranged by allowing the tip 37a, that is to say the free end of the outer part of spring 37, to come to rest against a projection or stop 42 on the foundation 36. At the same time the silver strip 31 will be resting on the electrodes 30a and 30b. The distance or airspace between magnet 40 and armature 41 has thus been fixed at a small value 6. The screw 43 is a stop to prevent the piston 9 from moving too far out and damaging the leaf spring 37. The aluminum walls of the chamber 27 should be covered with a thin film of an electrically insulating material. This is suitably achieved with aluminum oxide formed by electrolysis, the pores of which are filled by dipping casing 2 in Araldite.

If the temperature in the refrigerator is allowed to vary :1" C. at the most, then for normal efliciency the diameter of piston 9 is suitable about 6 mm., its stroke 'the elastic mica disc 29.

inwards towards the rubber 1.

spring 37, which presses against the piston 9 through The temperature now rises slowly. The piston 9 moves slowly outwards or toward the left in FIG. 1 and the inner part of leaf spring 37 gives way elastically. This causes the outer part of the spring 37 to be moved downwardly and the magnet 40 to approach the armature 41. The magnetic attraction between the magnet 40 and the armature 41 therefore increases, causing the leaf spring 32 to bend elastically a little in an upward direction and the outer part of leaf spring 37 to do the same downwards, with reference to FIG. 1. Thus magnet and armature move nearer still to each other. At a certain distance between them their equilibrium becomes unstable. The armature 41 is then thrown upwards, and the circuit is completed between the electrodes 30a and 30b through the silver strip 31. Simultaneously the magnet MB is thrown downwards, and the outer part of leaf spring 37 is elastically bent still further downwards. The magnets movement is then halted by the mechanical stop on the foundation, i.e., when the tip 37a meets the projection 42. The distance or airspace between magnet and armature has now achieved its minimum value 6, as mentioned above.

When the temperature falls the piston 9 moves slowly It (9) is forced in by the inner bulging part of the leaf spring 37. This causes the outer part to become still more bent, i.e., a little more work still is stored up in it. The tip 37a is still at rest on the stop 42, so that the airspace 5 and therefore also the contact pressure between the silver strip 31 and the electrodes 30a and 30b remain practically constant.

On the other hand the contact pressure between the tip 37a and the stop 42 decreases. When it has become nil, the position of equilibrium once again becomes unstable. The outer part of leaf spring 37, which has been bent by the magnetic attraction and also by virtue of the return movement of the piston, now suddenly straightens itself. The work stored in this outer part is suddenly freed. The magnet is thrown upwards. The magnetic attraction thus decreases and the leaf spring 32 also reverts to its normal shape. instantaneously. As can be seen, the outer and inner parts of leaf spring 37 perform quite different functions. The leaf spring 37 has two functions to perform. This is fundamental to achieve simplicity of construction.

The magnet and armature may of course be interchanged. Since the armature is lighter than the magnet however, the contact break will be quicker if they are placed as described.

It has been mentioned that the leaf spring 37 is angled The circuit is thus broken in shape, and it will be seen from FIG. 1 that it takes the approximate form of a right angle. This is necessary in order that the dimensions of the thermostat shall be small. Were the outer part of leaf spring 37 perpendicular to the geometric axis of the casing 2, as is its inner part, the diameter of the casing should then have to be to a certain value the leaf springs 11 begin to be compressed. By this means the casing 2 is prevented from being damaged by too great internal positive pressure. 7

The rubber piece 1 should be lubricated with silicon the pressure in the rubber mounts. When it has risen grease before being fitted into the casing 2. It will then move readily against the walls of the casing, and will also in chamber 27. By virtue of this the are on breaking direct current will be reduced, which is an advantage; Of less importance for a refrigeration thermostat is the fact that the increased pressure enables greater direct currents to be dealt with. Even with a pressure of only one atmosphere in chamber 27, and if the latter is 18 mm. in diameter, it is possible to break a circuit carrying a direct current of 6 amps at 220 volts.

It is desirable to be the Araldite plug 34 set in either a low temperature (which is now possible) or under very high pressure from the surrounding atmosphere or other surrounding medium. This will reduce the tension in the plug in ordinary function. Or further, stress could be imparted to it in place of tension, which would be advantageous.

When the piston 9 moves out and in with'variations in temperature, the rubber gets very slightly worn. Therewith a fine powder of rubber is formed, which gets squeezed into the narrow space between the part of the piston 9c and its cylinder. The loss of rubber is so slight that in practice this can be ignored. What cannot be as the increase in braking force in a band brake is an exponential function of the length of the band. The value of h should therefore be as little as possible. it should not be greater than the radius of the piston, and it is desirable that it should be of it or less, as stated above. The rubber powder collects in the small space 10. The friction between the piston 9 or its part and the rubber piece 1 is very small. The part 90 does not need to protrude any notable distance into the rubber, since its maximum stroke is not fully 0.1 mm.

The internal friction in the rubber is reduced in that the solid wall in the vicinity of the part 9c of the pistin is not plane, but conic. Surface 6 then is conic. The rubber can thus move elastically to or from the part 90 of the piston. The movement of the rubber is restricted if the conic surface is replaced by a plane one coincidental with the plane of the small surface 8. This phenomenon is related to and may be explained by the fact that any small portion of the rubber can elastically move more easily near the centre of gravity of the rubber piece than near a solid wall. f

The movement of the piston 9 could of course emanate from something other than rubber. The sensory component may for instance be a metal shaft within a metal tube where shaft and tube have different coefficients of expansion, in the known way. In a similarly known way both are fixed elastically to the thermostat casing so that 'the spring 37 and the foundation 36 of the electrical conthe rubber 1. The contact is thus made with a fall and broken with a rise in temperature. Otherwise the process is analogous with that of the refrigeration thermostat.

What I claim is:

1. An electric circuit breaker comprising, a housing containing a thermally-responsive material, a piston urged into contact with such material, a fixed electrical contact located within the housing, a leaf spring carrying a movable contact and also carrying a magnetic armature, a second leaf spring carrying a magnet, abutment means for limiting movement of the second leaf spring in a direction toward the first leaf spring, the second leaf spring having a part operative against the piston whereby said second leaf spring will be initially urged toward the abutment means by piston-pressure against said part of the leaf spring when the piston is moved under thermal expansion of the thermally-responsive material.

2. An electric circuit breaker comprising, a thermallyresponsive element, a pair of leaf springs, one of which carries an electrical contact, a fixed contact against which the spring-borne contact abuts upon movement of the contact-bearing spring to a predetermined position, cooperating magnetic elements respectively carried by the springs and effective to hold the springs in a position wherein the contacts are in abutment, one of the springs having a portion so disposed in relation to the thermallyresponsive element, that said element, in response to thermal changes, will cause movement of said spring to a position wherein the magnetic element carried by it will influence the magnetic element carried by the other spring to thereby cause the contact-carrying spring to be moved to bring its contact against the fixed contact.

3. An electric circuit breaker comprising, a housing containing a body of thermally-responsive rubber, spring means arranged at one end of the rubber, means for varying the pressure of said spring means on the rubber, a disc at the opposite end of the rubber, said disc having an axial opening, a piston arranged in said opening and having one of its ends in contact with the rubber, a leaf spring having a part in contact with the opposite end of the piston but insulated therefrom, said leaf spring having a projecting arm bearing a magnetic element, a second leaf spring carrying an electrical contact and also carrying a magnetic element adapted to be influenced by the magnetic element carried by the first spring, a fixed contact in the housing adapted for abutment with the spring-borne contact, and stop means for limiting the movement of the arm in a direction toward the second leaf spring so that air space exists between the magnetic elements when the contacts are touching one another,

4. An electric circuit breaker as provided for in claim 3, wherein the piston is provided with a central part having its periphery spaced from the inner Wall surface of the axial opening in the disc so that rubber particles displaced by the sliding action of the piston can be collected to thereby avoid frictional resistance to piston movement.

5. An electric circuit breaker as provided for in claim 3, wherein the disc at one end of the rubber has its axial opening disposed in a central hub, the outer surface of which is conical and which hub enters into the rubber body.

6. In a circuit breaker, a thermally-responsive element, a spring-borne magnet acted on by said element to thereby move the magnet, a fixed contact, a movable contact acted on by the magnet and normally maintained in open position by a spring whose force in the closed position of the contacts is less than that exerted by the magnet, a base for supporting the magnet-bearing spring and the second-mentioned spring, said base providing abutment means for limiting movement of the magnetbearing spring in a direction toward the second spring when the magnet-bearing spring is moved in said direction under the influence of the thermally-responsive element so that an air gap is produced between the magnet and the second spring at the limit of movement of the magnet-bearing spring toward the second spring.

References Cited in the file of this patent UNITED STATES PATENTS 1,890,909 Lincoln Dec. 13, 1932 2,548,941 Brown Apr. 17, 1951 2,659,787 Prickett Nov. 17, 1953 2,750,474 Gray June 12, 1956 2,990,716 Butts July 4, 1961 3,007,029 Levine Oct. 31, 1961 

1. AN ELECTRIC CIRCUIT BREAKER COMPRISING, A HOUSING CONTAINING A THERMALLY-RESPONSIVE MATERIAL, A PISTON URGED INTO CONTACT WITH SUCH MATERIAL, A FIXED ELECTRICAL CONTACT LOCATED WITHIN THE HOUSING, A LEAF SPRING CARRYING A MOVABLE CONTACT AND ALSO CARRYING A MAGNETIC ARMATURE, A SECOND LEAF SPRING CARRYING A MAGNET, ABUTMENT MEANS FOR LIMITING MOVEMENT OF THE SECOND LEAF SPRING IN A DIRECTION TOWARD THE FIRST LEAF SPRING, THE SECOND LEAF SPRING HAVING A PART OPERATIVE AGAINST THE PISTON WHEREBY SAID SECOND LEAF SPRING WILL BE INITIALLY URGED TOWARD THE ABUTMENT MEANS BY PISTON-PRESSURE AGAINST SAID PART OF THE LEAF SPRING WHEN THE PISTON IS MOVED UNDER THERMAL EXPANSION OF THE THERMALLY-RESPONSIVE MATERIAL. 